Demolition firing device

ABSTRACT

A firing device is sympathetically activated by the pressure wave generated by a nearby air or underwater explosion. When activated, the firing device detonates a main charge to which it is attached and the resultant shock wave initiates a similar firing device in cain reaction fashion. An incoming pressure wave is converted into an electrical signal by a hydrophone, amplified by an FET amplifier, and level detected by a programmable unijunction transistor. If the pressure wave is above a predetermined amplitude, the programmable unijunction transistor conducts, causing an SCR to become conductive. This allows a firing capacitor to discharge through an explosive primer, which in turn detonates a main charge. The firing device also includes delay arming circuitry and self-destruct circuitry.

0 United States Patent 1191 [111 3,741,124 Visk June 26, 1973 DEMOLITION FIRING DEVICE 75 Inventor: Francis A. Visk, Beltsville, Md. ABSTRACT 73 Assignee; Th Uni/ed states of America as A firing device is sympathetically activated by the presrepresemed by the secretary f the sure wave generated by a nearby air or underwater ex- Navy, Washington D plosion. When activated, the firing device detonates a main charge to wich it is attached and the resultant [22] Med: 1 1971 sock wave initiates a similar firing device in chain reac- [21] Appl. No.2 143,679 tion fashion. An incoming pressure wave is converted into an electrical signal by a hydrophone, amplified by 52 0.8. Ci. 102/70.2 R 18l/0.5 340/16 0 FET amplifier and level detected by Pmg'amma' 340/5 42 c 6 ble unijunction transistor. If the pressure wave is above 511 Int. Cl F42c 11/02 F421: 9/16 ampliwdethe Pmgmmmable [58] Field of Search 162/702 18' causing SCR 4 6 C 7 come conductive. This allows a firing capacitor to discharge through an explosive primer, which in turn det- [56] References Cited onates a main charge. The firing device also includes UNITED STATES'PATENTS delay arming circuitry and self-destruct circuitry. 3,572,244 3/1971 Garber 340/ 16 C 3,027,837 3/1962 Kendall 340/16 C Primary ExaminerBenjamin A. Borchelt 8 Claims, 3 Drawing Figures Asristqnt Examiner-Thomas B. Webb Attorney-R. S. Sciascia, J A. Cooke, R. J. Erikcson and K.

E. Krosin IO l2 l4 7 l6 I8 20 r r 1 g 1 PRESSURE- TRANS FE LEVEL PRIMER SIGNALS, DUGER AMP DETECTOR ClRCUlT l l l 24 /26 f POWER 32 SAFING SUPPLY a fi ARMlNG TlMER DEVICE I O'T- DELAY ARMING 22 VOLTAGE I REGULATOR MAIN i I TIMER CHARGE 0T SELF I DISTRUCT I Pmmzmunzs Ian 3.741.124

SHEEI 1 0f 2 l0 l2 l4 j l6 I8 20 I l I I l PRESSURE- TRANS- FET LEVEL FIRING sls-ALs/ DUCER AMP DETECTOR cmcun' 4 4 f l 4 26 2 POWER 3O 32 SUPPLY SAFaING I TlMER ARMING 0- DELAY l i ARMING 22 34 VOLTAGE REGULATOR I I Mm l CHARGE {2 I SELF I DISTRUCT I I o L l PESSURE A A 4 V INVENTOR FRANCIS A. V/SK FIG. 2.

I f 190. /6 AGENT DEMOLITION FIRING DEVICE BACKGROUND OF THE INVENTION This invention relates generally to firing devices for explosives, and more particularly to acoustically activated firing devices for explosives. Previous methods of detonating a series of charges involved the stringing of electrical firing leads or detonating cords to each charge in a multi-charge detonating mission. As a result, prior art systems have several inherent disadvantages. First, these systems are unreliable, since it is not always possible 'to exercise great care in stringing the series of charges together. Any fault in the electrical cord or faulty connections at any given charge prevents detonation of all succeeding charges in the series array. Second, these prior art systems are relatively unsafe. Bearing the cumbersome cord to the objective and spending extended periods of time in wiring each individual charge unduly exposes the person performing the installation. The possibility of accidental detonation by careless handling or incorrect wiring is always present. Third, it is difficult to install the prior art systems, since usually each charge is first placed at the desired position, and then all of the charges are wired together in a series configuration. Finally, these systems are expensive, since the cost of the cord is a significant part of the overall cost of the system.

SUMMARY OF THE INVENTION Accordingly, one object of the instant invention is to provide a new and improved firing device for detonating a series of explosives.

Another object of the instant invention is the provision of a firing device for a series of explosives that can be easily installed.

Still another object of the present invention is the provision of a safe firing device for a series of explosives.

A further object of the instant invention is to provide an inexpensive firing device for a series of explosives.

A still further object of the present invention is the provision of an acoustically activated firing device.

Briefly, in accordance with one embodiment of this invention, these and other objects are obtained by providing a demolition firing device that transduces acoustic pressure waves into electrical signals, amplifies and level detects the resultant electrical signals, and energizes an explosive primer if the detected electrical signal is above a predetermined amplitude. The explosive primer then detonates through a safing and arming device a main charge, and the resulting explosion creates an acoustic pressure wave that can be used to activate a similar nearby firing device.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagrammatic view of the demolition firing device of the present invention;

FIG. 2 is a curve of the signature of a pressure wave produced by a high explosive; and

FIG. 3 is a schemetic diagram of the demolition firing device of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, a demolition firing device is shown receiving pressure signals. As described hereinafter, demolition firing device 10 is suitable for use in air or underwater. Thus, the pressure signals are transmitted either through an air medium or a water medium. These pressure signals strike a conventional pressure tranducer 12, such as a hydrophone, and are converted into electrical signals. When high explosives, such as TNT, are detonated, a shock wave is propagated through the medium. As shown in FIG. 2, the pressure signature of this wave is characterized by a steep leading edge of a considerable magnitude. Pressure transducer 12 generates electrical signals in response to this over pressure which are fed to a field effect transistor (FET) amplifier 14. As described hereinafter with reference to FIG. 3, PET amplifier 14 low pass filters these electrical signals to remove high frequency components, attenuates the low pass filtered signals if the pressure signals are received through a water medium, and amplifies the resulting signals. The output of PET amplifier 14 is supplied to a level detector 16, described hereinafter with reference to FIG. 3, that generates an output signal if the signal from FET amplifier 14 is above a predetermined level. This predetermined level is selected so that ambient pressure signals do not produce an output from level detector 16. Only relatively high pressure signals, such as produced by the aforementioned high explosives, will produce an output from level detector 16.

The output from level detector 16 is a pulse which is applied to a firing circuit 18, described hereinafter with reference to FIG. 3, which generates a firing pulse. This firing pulse detonates a conventional explosive primer 20 which is coupled to a conventional main explosive charge 22 through a conventional safing and arming device 24.

Operational power for demolition firing device 10 is supplied by a power supply 26, such as a battery, the output of power supply 26 is applied to a conventional voltage regulator 28 which insures a constant output voltage regardless of voltage fluctuations from power supply 26. A conventional triple pole, double throw mechanical switch 30 couples the output of voltage regulator 28 to a timer delay arming device 32, and simultaneously to a timer self-destruct device 34, both of which are described in greater detail hereinafter with reference to FIG. 3. The third section of switch 30 is connected between ground potential and primer 20. Prior to deployment of demolition firing device 10, switch 30 is in its disabled or safe position. Whereby an open circuit exists between voltage regulator 28 and timer delay arming device 32, an open circuit exists be tween voltage regulator 28 and timer self-destruct device 34, and the firing or hot lead of primer 20 is grounded. Thus, no power is supplied to the remaining circuit elements, and primer 20 is grounded to prevent spurious actuation, such as by a stray electromagnetic or electrostatic field.

With switch 30 in its other position, power is supplied to timer delay arming device 32 and timer self-destruct device 34 by voltage regulator 28, and the firing lead to 20 is disconnected from ground potential. The output of timer delay arming device 32 is coupled to FET amplifier 14, level detector 16, and firing circuit 18. Upon the closure of switch 30, operating power from voltage regulator 28 is prevented from reaching these circuits for a predetermined period of time by timer delay arming device 32. This time delay may be, for example, 30 minutes to allow deployment of demolition firing device 10 and evacuation from within its explosive range. After a longer predetermined period of time, such as 24 hours, timer self-destruct device 34 presents a closed circuit between voltage regulator 28 and the input to firing circuit 18, thereby causing demolition firing device 10 to self-destruct.

Referring now to FIG. 3, demolition firing device 10 is illustrated in greater detail. Incoming pressure signals strike pressure transducer 12 which is connected between a pair of input terminals 36 and 38. Terminal 38 is connected to ground potential, and the resulting transduced electrical signals appear at terminal 36. These signals are applied to FET amplifier 14, as described hereinbefore. The input circuitry of PET amplifier 14 comprises a low pass filter consisting of a resistor 40 connected at one end to input terminal 36 and a capacitor 42 connected between the other end of resistor 40 and ground. The output of this low pass filter appears at a junction point 44 between resistor 40 and capacitor 42. In the preferred embodiment of the instant invention, pressure transducer 12 is of relatively simple construction and inexpensive, and, consequently, has a relatively flat frequency response over a limited range of frequencies, for example to 3,000 Hz. Above 3,000 Hz the frequency response may become extremely nonlinear, and it is the purpose of the low pass filter defined by resistor 40 and capacitor 42 to filter out all of the electrical signals above this critical frequency.

A resistor divider network 46 consisting of series connected resistors 48 and 50 is connected in parallel with capacitor 48 between junction point 44 and ground. A capacitor 51 connected in parallel with resistor 50 filters out any additional high frequency signals. Electrical signals appearing at junction point 44 are directly coupled to a first terminal 52 in a conventional single pole, double throw swtich 54, and through resistor 48 to a second terminal 56 in switch 54. Thus, the signal appearing at terminal 52 is unattenuated, equal to the signal appearing at junction point 44, while the signal appearing at terminal 56 is attentuated by the action of resistor divider network 46. In one position, the arm of switch 54 connects terminal 52 to the gate of a conventional P-channel field effect transistor FET 58, while in its other position, the arm of switch 54 connects terminal 56 to the gate of PET 58. These alternative inputs to FET 58 are provided because of the different environments in which demolition firing device may be used. Under normal conditions, water is a superior medium to air for the transmission of pressure signals. Consequently, for a specified distance between a pressure wave source and a demolition firing device 10, the pressure wave arriving at transducer 12 will have a higher amplitude when transmitted through water, than through air. This, in turn, will produce greater amplitude electrical signals at junction point 44 for water as opposed to air. To normalize the signal level for air and water operation, terminal 52 is connected to the gate of FET 58 when demolition device 10 is used in an air environment, and terminal 56 is connected to the gate of PET 58 when demolition firing device 10 is used underwater. Thus, the difference in transmissive characteristics between water and air is compensated by proper selection of the values of resistors 48 and 50.

A field effect transistor is employed in amplifier 14 because of its extremely high input impedance which prevents loading on the aforedescribed circuitry. A resistor 62 is connected between the drain terminal of PET 58 and ground, and a resistor 64 is connected between the source terminal of PET 58 and timer delay arming device 32, described hereinafter. The output of PET amplifier 14 is taken from the source terminal of PET 58 and applied to the gate of a programmable unijunction transistor (PUT) 66 in level detector 16. A resistor 68 is connected to one end to the anode of PUT 66 and at the other end to one end ofa resistor 70. The other end of resistor 70 is connected to timer delay arming device 32. Resistor 70 limits the current to firing circuit 18 to prevent primer detonation if one of the elements in firing circuit 18 is short circuited to primer 20. A variable resistor 72 connected between the anode of PUT 66 and ground sets the potential at which PUT 66 fires by setting the anode potential of PUT 66. If the voltage at the gate of PUT 66 drops more than approximately 0.7 volts below the anode potential of PUT 66, PUT 66 produces an output pulse at its cathode which is applied to firing circuit 18. By having a variable firing level for PUT 66, the sensitivity of demolition firing device 10 to incoming pressure signals can be varied over a wide range.

The firing pulse from PUT 66 is coupled through a capacitor 74 to the gate of a silicon controlled rectifier (SCR) 76 in firing circuit 18. The anode of SCR 76 is connected to the junction point between resistors 68 and 70, and its cathode is connected to the firing or hot lead of primer 20. A resistor 77 is connected between the gate of SCR 76 and ground, firing capacitor 78 is connected between the anode of SCR 76 and ground potential. With SCR 76 normally nonconducting, firing capacitor 78 charges to the potential between resistor 68 and 70. When SCR 76 becomes conductive in response to a firing pulse from PUT 66, capacitor 78 discharges through SCR 76 and primer 20 to ground, thereby causing primer 20 to detonate. If safing and arming device 24 is conditioned to allow detonation, main charge 22 detonates in response to the detonation of primer 20.

To prevent tampering with demolition firing device 10, a conventional trembler switch 80 is connected between the anode and gate of SCR 76. If demolition firing device 10 is physically jostled or disturbed, trembler switch 80 momentarily closes, thereby applying the supply potential for firing circuit 18 obtained from the junction between resistors 68 and 70 to the gate of SCR 76. This in turn causes SCR 76 to conduct and capacitor 78 to discharge through SCR 76 and detonate primer 20, as described hereinbefore.

Timer delay arming device 32 and timer self-destruct device 34 are both conventional electrochemical delay arming switches which close contacts after a predetermined period of time. Referring to timer delay arming device 32, for example, operation of switch 30 to its active position allows a current to flow from voltage regulator 28 through switch 30, a resistor 84, and an electrochemical section 86 of timer delay arming device 32. Electrochemical section 86 is coupled to a spring loaded contact bar 88 in a well known manner. After a pre-determined amount of current has passed through the electrochemical section 86, contact bar 88 is released, causing it to short together a pair of terminals 90 and 92. Terminal 90 is connected to voltage regulator 28, and terminal 92 is connected to the common junction between resistors 64 and 70. Thus, by

shorting together terminals 90 and 92, power is supplied to FET amplifier 14, level detector 16, and firing circuit 18. Resistor 84 and the voltage level of voltage regulator 28 control the amount of current flowing through electrochemical section 86. Consequently, the value of resistor 84 and the regulated voltage level determine the time delay between the closure of switch 30 and the shorting together of terminals 90 and 92. Timer self-destruct device 34 operates in the same manner as timer delay arming device 32 to short circuit a pair of terminals 94 and 96. Terminal 94 is connected to the positively charged side of capacitor 78, and terminal 96 is connected to the hot lead of primer 20. Consequently, short circuiting of terminal 94 and 96 causes capacitor 78 to discharge through these terminals to primer 20, thereby producing detonation as described hereinbefore. A timing resistor 98 coupled to the electrochemical section of timer self-destruct device 34 and the regulated voltage level determine the time delay between the closure of switch 30 and the shorting together of terminals 94 and 96. Since timer delay arming device 32 operates to short circuit terminals 90 and 92 relatively soon after the deployment of demolition firing device 10, and timer self-destruct device 34 operates to short circuit terminals 94 and 96 after demolition firing device has been deployed for s substantial period of time, it should be apparent that resistor 98 is of substantially greater resistance than resistor 84.

In operational use, it is envisioned that two or more demolition firing devices according to the present invention be deployed over an area such that each is within the detection range of an explosion produced by at least one other demolition firing device. After the delay arming interval determined by timer delay arming device 32, a starter explosive is detonated within the detection range of at least one of the demolition firing devices. This explosion produces a pressure signal which causes that demolition firing device to detonate. Detonation of that firing device in turn produces a pressure wave that detonates nearby demolition firing devices. By chain reaction all of the-demolition firing devices are detonated within a short period of time, determined by the spacing between the demolition firing devices and the speed of propagation of the pressure wave through the particular medium. If no starting charge is detonated, the first demolition firing device to self-destruct, as determined by timer self-destruct device 34, will provide the initial explosion to trigger the remaining demolition firing devices. If, by mistake, one or more demolition firing devices have been placed at too great a distance from other demolition firing devices so that the pressure signals received by them are insufficient to produce detonation, these demolition firing devices will independently self-destruct after the period of time determined by timer self-destruct device 34. Thus, by employing demolition firing devices of the presnt invention, it is possible to lay a land or water mine field or series of charges that are not connected physically, but which nevertheless detonate in chain reaction or series fashion.

Obviously, numerous modifications and variations of the present invention are possible in light of the above 6 teachings. For example, other types of well known delay arming switches may be used. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

l. A demolition firing device comprising:

transducer means for transducing pressure signals into electrical signals;

means coupled to said transducing means for filtering and amplifying said electrical signals;

level detecting means coupled to said filtering and amplifying means for generating an output pulse whenever the output of said filtering and amplify.- ing means exceeds a predetermined variable voltage amplitude;

firing means connectable to an electrically activated explosive primer and coupled to said level detecting means for supplying a firing pulse to said explosive primer in response to said output'pulse; and

electromechanical arming delay switch means connectable to a source of electrical potential connected for applying said electrical potential to said filtering and amplifying means, said level detecting means, and said firing means after a first predetermined period of time.

2. The demolition firing device of claim 1, wherein said transducer means comprises a hydrophone.

3. The demolition firing device of claim 1, wherein said filtering and amplifying means comprises;

a low pass filter coupled to said transducer means;

and

means for amplifying the output of said low pass filter.

4. The demolition firing device of claim 3, wherein said amplifying means comprises:

a resistor deivider network coupled across the output of said low pass filter and providing a plurality of output signals;

switching means for selecting any one of said plurality of output signals; and

a field effect transistor amplifier for amplifying said selected one of said plurality of output signals.

5. The firing device of claim 1, wherein said level detecting means comprises:

a programmable unijunction transistor having its gate coupled to the output of said filtering and amplifying means and producing said output pulse at its cathode; and

means for biasing the anode of said programmable unijunction transistor to a selectable potential to establish said predetermined variable voltage amplitude.

6. The demolition firing device of claim 5, wherein said biasing means includes a variable resistance connected to the anode of said programmable unijunction transistor and connectable to a source of reference potential.

7. The demolition firing device of claim 1, wherein said firing means comprises:

a silicon controlled rectifier having its gate coupled to the output of said level detecting means, having its cathode connectable to said explosive primer, and having its anode connectable to said source of electrical potential;

a firing capacitor connected to the anode of said silicon controlled rectifier and connectable to a source of reference potential;

LII

ond predetermined period of time.

8. The demolition firing device of claim 7, wherein said antitampering means comprises a trembler switch connected between the anode and gate of said silicon controlled rectifier. 

1. A demolition firing device comprising: transducer means for transducing pressure signals into electrical signals; means coupled to said transducing means for filtering and amplifying said electrical signals; level detecting means coupled to said filtering and amplifying means for generating an output pulse whenever the output of said filtering and amplifying means exceeds a predetermined variable voltage amplitude; firing means connectable to an electrically activated explosive primer and coupled to said level detecting means for supplying a firing pulse to said explosive primer in response to said output pulse; and electromechanical arming delay switch means connectable to a source of electrical potential connected for applying said electrical potential to said filtering and amplifying means, said level detecting means, and said firing means after a first predetermined period of time.
 2. The demolition firing device of claim 1, wherein said transducer means comprises a hydrophone.
 3. The demolItion firing device of claim 1, wherein said filtering and amplifying means comprises; a low pass filter coupled to said transducer means; and means for amplifying the output of said low pass filter.
 4. The demolition firing device of claim 3, wherein said amplifying means comprises: a resistor deivider network coupled across the output of said low pass filter and providing a plurality of output signals; switching means for selecting any one of said plurality of output signals; and a field effect transistor amplifier for amplifying said selected one of said plurality of output signals.
 5. The firing device of claim 1, wherein said level detecting means comprises: a programmable unijunction transistor having its gate coupled to the output of said filtering and amplifying means and producing said output pulse at its cathode; and means for biasing the anode of said programmable unijunction transistor to a selectable potential to establish said predetermined variable voltage amplitude.
 6. The demolition firing device of claim 5, wherein said biasing means includes a variable resistance connected to the anode of said programmable unijunction transistor and connectable to a source of reference potential.
 7. The demolition firing device of claim 1, wherein said firing means comprises: a silicon controlled rectifier having its gate coupled to the output of said level detecting means, having its cathode connectable to said explosive primer, and having its anode connectable to said source of electrical potential; a firing capacitor connected to the anode of said silicon controlled rectifier and connectable to a source of reference potential; anti-tampering means for connecting the gate of said silicon controlled rectifier to said source of electrical potential in response to physical movement of said demolition firing device; and self-destruct means for directly discharging said firing capacitor through said explosive primer after a second predetermined period of time.
 8. The demolition firing device of claim 7, wherein said antitampering means comprises a trembler switch connected between the anode and gate of said silicon controlled rectifier. 